Java timer (Timer, TimerTask) detailed explanation and example code

Java Timer

The two classes used to implement the timer function in JAVA are Timer and TimerTask

The Timer class is a class used to perform tasks. It accepts A TimerTask takes parameters

Timer has two modes for executing tasks. The most commonly used is schedule, which can execute tasks in two ways: 1: at a certain time (Data), 2: at After a fixed time (int delay). Both methods can specify the frequency of task execution. There are two examples in this article, one is simple and the other uses the internal class

1. Simple example

First write a class

public class TimeTest {
public static void main(String[] args) {
   
   Timer timer = new Timer();
   timer.schedule(new MyTask(),1000,2000);
}

and then write a class

public class MyTask extends TimerTask{
 
  @Override
  public void run() {
 System.out.println("开始运行");    
  }
}

This way you can complete a simple timer, but there is another way to combine these two A class is written into a class, which is an internal class.

2. Internal class

public class SerchRun {
 
  protected static void startRun(){
    Timer timer = new Timer();
     TimerTask task =new TimerTask(){
       public void run(){
         System.out.println("开始运行"); //在这写你要调用的方法
       }
     };
   timer.scheduleAtFixedRate(task, new Date(),2000);//当前时间开始起动 每次间隔2秒再启动
   // timer.scheduleAtFixedRate(task, 1000,2000); // 1秒后启动 每次间隔2秒再启动         
   }
   
  public static void main(String[] args) {
   SerchRun.startRun();
  }
}

The difference between schedule and scheduleAtFixedRate is that if the specified start time of execution is before the current system running time , scheduleAtFixedRate will execute the elapsed time as a period, but schedule will not count the elapsed time.

For example:

SimpleDateFormat fTime = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
 Date d1 = fTime.parse("2005/12/30 14:10:00");
  
 t.scheduleAtFixedRate(new TimerTask(){
  public void run()
  {
    System.out.println("this is task you do6");
  }
 },d1,3*60*1000);

The interval is 3 minutes, and the specified start time is 2005/12/30 14:10:00. If I execute this program at 14:17:00, then

this is task you do6   //14:10
this is task you do6   //14:13
this is task you do6   //14:16

will be printed three times immediately and note that the next execution is at 14:19 instead of 14:20. That is to say, timing starts from the specified start time, not from the execution time.

But if the schedule method is used above, the interval is 3 minutes, and the specified start time is 2005/12/30 14:10:00, then if the program is executed at 14:17:00, the program will be executed immediately once. And the next execution time is 14:20, not the period starting from 14:10 (14:19).

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